| Summary: | 碩士 === 國立屏東科技大學 === 土木工程系所 === 95 === In Taiwan, rainfall is alternately affected by typhoons in summer and monsoons in winter. During the summer typhoons thunderstorms occur regularly, producing most of the rainfall, while during the winter the monsoons cause a dry season. The rainy season lasts from May to October. Rainfall in the remaining six months amounts to only about 10% of the total. However, during the rainy season, surface water with mud and sand are flown to the rivers, leading to an excessively high turbidity of water source. When the turbidity of water is high that even the water quality cannot be improved by the purification plant, a shortage of water or a reduced water supply shall be affected. It is common to find a water shortage in the period of dry season. Nevertheless, during the rainy season if there is a water shortage caused by the high turbidity of river water, it is obviously unreliable to deliver surface water as source for drinking water.
The way to separate liquid and solids from the high turbidity water is filtration, including the use of natural filtration bed and the artificial spreading of filtration layer. The research based on Darcy’s law and chemical change of the soils contrasts the coefficients of permeability of quartz sand, and sand sample in the upstream/ downstream of Kaoping River, and exams their filtered water. This study analyzes and compares the examinations of the water source in the Kaoping River and these three kinds of filtered water mentioned above to obtain their removal rates.
In the laboratory, at the bottom of a one-meter-high sand box is successively spread with filtration sand for the thickness of 21cm, installed with the first infiltration pipe, spread with the second layer of filtration sand for the thickness of 18cm, installed with the second infiltration pipe, spread with the third layer of filtration sand for the thickness of 18cm, installed with the third infiltration pipe, spread with a layer of filtration sand for the thickness of 18cm above the third filtration pipe, with a total thickness of filtration sand reaching 75cm, and then poured in the water source of Kaoping River onto the surface of the top layer of filtration sand. After that, the filtered water is pumped out for experiment. It is found that the turbidity of water is reduced by 69~ 87%, the removal rate of ammonia nitrogen reaches 93~94%, the removal rate of nitrate nitrogen is 75~98%，the removal rate of iron is 67~100%, and the removal rate of manganese is 57~82%. Under the circumstances that the water flow is not disturbed, the Suspended Solid is reduced from 10.2mg/L to 3.2mg/L.The others such as Total Dissolved Solid, Total Hardness et al, are also slightly reduced.This experiment has been proved that with the help of natural filtration bed and artificial spreading of filtration layer, the infiltration pipe authorized by the German manufacturer and made in Taiwan can be applied to the pumping of water below the riverbed to acquire water of better quality.
Keywords: filtration, turbidity, Darcy’s Law , Suspended Solid.
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